This invention relates to a filter, and more particularly to an improved ceramic filter of the distributed constants type having a substrate of a dielectric with a high dielectric constant. Such a filter is very effective as a band-rejection filter over a wide range from the UHF to the SHF frequency band, and also it can also be used effectively to remove the undesired high frequency signal for an electronic circuit operating in the VHF or microwave range or to protect electronic equipment against a high frequency from a high frequency power source circuit the electronic equipment uses.
Conventional filters of the lumped constants type, which are formed by conventional discrete components such as a capacitor and a coil, do not perform well as a high frequency band-stop filter for the VHF band or the microwave range, and so usually there are used various filters using components such as a pair of parallel-coupled lines, coaxial lines and a wave guide tube, as a distributed constants type high frequency filter rather than a lumped constants type filter.
However, these conventional high frequency filters of the distributed constants type have some defects. That is, because very hige precision is required for these lines or the waveguide, the filters cannot be designed and manufactured practically with ease. Furthermore, because expensive materials are used for these lines or the waveguide, they cause increased consts in the manufacturing process. In addition, for achieving filter characteristics of operation over a wide frequency band and high performance such as a high electrical quality factor Q, it is inevitable that the construction of the filter circuit is inevitably inclined to be large in size.